How do I make an armature skeleton?
After selecting your armature, go into edit mode and select the bone you want to join to your master bone (in your case, the lowest is your master bone). While in edit mode, go to:

Properties &gt;&gt; Bone &gt;&gt; Relations 

and under "Parent", select the master bone and tick the "Connected" box. If you haven't named your bones, you might have to try all of them but luckily you've only got 3.